Led lamp

ABSTRACT

An LED lamp includes a substrate, an LED chip, and a resin portion. The LED chip is flip-chip bonded to the substrate. The resin portion covers the LED chip and includes at least one type of phosphor that transforms the emission of the LED chip into light having a longer wavelength than the emission. In this LED lamp, the resin portion has at least one side surface. The side surface is separated from another surface that can reflect the outgoing light of the resin portion, surrounds the side surfaces of the LED chip and is curved at least partially.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an LED lamp including an LEDchip, which is covered with a resin portion containing a phosphor, andalso relates to a method for fabricating such an LED lamp.

[0003] 2. Description of the Related Art

[0004] White LED lamps are recently under vigorous research anddevelopment as potential replacements for white incandescent lamps. Insome of those white LED lamps, the package of a blue LED chip, made ofgallium nitride (GaN), is coated with a phosphor such as YAG. In such anLED lamp, the blue LED chip produces an emission with a wavelength ofabout 450 nm, and the phosphor produces yellow fluorescence with a peakwavelength of about 550 nm on receiving that emission. Eventually, theemission and fluorescence mix with each other, thereby providing whitelight.

[0005] In another type of white LED lamp currently under development, anLED chip that emits an ultraviolet ray is combined with a phosphor thatproduces red (R), green (G) and blue (B) light rays. In such an LEDlamp, the ultraviolet ray that has been radiated from the LED chipexcites the phosphor, thereby emitting the red, green and blue lightrays. Consequently, white light can also be obtained as a mixture ofthese light rays.

[0006] A bullet-shaped package is extensively used in conventional LEDlamps. Hereinafter, such an LED lamp with a bullet-shaped appearancewill be described with reference to FIG. 1.

[0007]FIG. 1 illustrates a cross-sectional structure for a conventionalLED lamp 20 as disclosed in Japanese Patent No. 2998696, for example. Asshown in FIG. 1, the LED lamp 20 includes an LED chip 21, abullet-shaped transparent housing to cover the LED chip 21, and leads 22a and 22 b to supply current to the LED chip 21. A cup reflector 23 forreflecting the emission of the LED chip 21 in the direction indicated bythe arrow D is provided for the mount portion of the lead 22 b. Theinner walls (i.e., reflective surfaces) of the cup reflector 23 surroundthe side surfaces of the LED chip 21 so as to define a predeterminedtilt angle with respect to the bottom of the cup reflector 23. The LEDchip 21 on the mount portion is encapsulated with a first resin portion24, which is further encapsulated with a second resin portion 25.

[0008] The first resin portion 24 is obtained by filling the cupreflector 23 with a resin material and curing it after the LED chip 21has been mounted onto the bottom of the cup reflector 23 and then hashad its cathode and anode electrodes electrically connected to the leads22 a and 22 b by way of wires. A phosphor 26 is dispersed in the firstresin portion 24 so as to be excited with the light A that has beenemitted from the LED chip 21. The excited phosphor 26 producesfluorescence (which will be referred to herein as “light B”) that has alonger wavelength than the light A. This LED lamp 20 is designed suchthat if the light A radiated from the LED chip 21 is red, then the lightB emitted from the phosphor 26 is yellow. A portion of the light A istransmitted through the first resin portion 24 including the phosphor26. As a result, light C as a mixture of the light A and light B is usedas illumination.

[0009] The conventional LED lamp shown in FIG. 1, however, has a colorunevenness problem.

[0010] In this LED lamp, the light C, obtained by mixing the light A andlight B together, is used as illumination as described above.Accordingly, color unevenness is easily created in the light C dependingon the shape of the first resin portion 24 including the phosphor 26.

[0011] In the conventional LED lamp 20, the first resin portion 24 isobtained by filling the cup reflector 23 with a resin material andcuring it such that the LED chip 21 is encapsulated with the resinmaterial. Thus, the shape of the first resin portion 24 is defined bythat of the internal recess of the cup reflector 23. In the LED lamp 20shown in FIG. 1, the reflective surfaces of the cup reflector 23 aretilted so as to define a downwardly tapered cross section. Accordingly,the upper surface of the resultant first resin portion 24 is broaderthan the lower surface thereof, and the side surfaces thereof make tightcontact with the reflective surfaces of the cup reflector 23. That is tosay, the cup reflector 23 is closely filled with the first resin portion24 so as to create no gaps between the first resin portion 24 and thecup reflector 23.

[0012] Specifically, the first resin portion 24 is obtained by pouring aresin liquid into the cup and curing it. For that reason, the uppersurface of the first resin portion 24 often becomes uneven as shown inFIG. 1. In addition, since the resin portion 24 has a downwardly taperedcross section, the upper surface of the resin portion 24 has arelatively broad area, thus creating significant effects. That is tosay, such unevenness on the upper surface of the first resin portion 24makes the thickness of the resin layer including the phosphor uneven. Inthat case, the amount of the phosphor included in one part of the resinportion 24 will be significantly different from that of the phosphorincluded in another part of the resin portion 24. In other words, theamount of the phosphor included changes according to the optical path ofthe light A being transmitted through the resin portion 24. As a result,quite noticeable color unevenness is created in the light C.

[0013] Furthermore, since the first resin portion 24 makes close contactwith the reflective surfaces of the cup reflector 23, the part of thefirst resin portion 24 surrounding the side surfaces of the LED chip 21has non-uniform, variable thicknesses. In that case, the light that hasgone out of the LED chip 21 through a side surface thereof is absorbedinto the phosphor in the first resin portion 24 in variable amountswhile being transmitted through the first resin portion 24 and beforereflected from the reflective surfaces. The amount of the light absorbedinto the phosphor also changes with the optical path thereof because thethicknesses of that part of the resin portion 24 are non-uniform. FIG. 2schematically shows the optical paths E and F of the light that has beenradiated through a side surface of the LED chip 21. As can be seen fromFIG. 2, when taking the optical path E, the light A needs to go arelatively short distance through the first resin portion 24. On theother hand, when taking the optical path F, the light A needs to go arelatively long distance through the first resin portion 24. The light Aradiated from the LED chip 21 is absorbed into the phosphor whileexciting the phosphor and making the phosphor radiate the light B.Accordingly, if the light A radiated from the LED chip 21 should godifferent distances through the first resin portion 24, then the mixtureratio of the light A and light B is changeable with the optical path. Asa result, significant color unevenness is created in the light C for useas illumination. The optical path length is often variable if the sidesurfaces of the first resin portion 24 are tapered to reflect theinternal shape of the cup reflector 23 as shown in FIG. 2.

SUMMARY OF THE INVENTION

[0014] In order to overcome the problems described above, preferredembodiments of the present invention provide an LED lamp with reducedcolor unevenness.

[0015] An LED lamp according to a preferred embodiment of the presentinvention preferably includes a substrate, an LED chip, and a resinportion. The LED chip is preferably flip-chip bonded to the substrate.The resin portion preferably covers the LED chip and preferably includesat least one type of phosphor that transforms the emission of the LEDchip into light having a longer wavelength than the emission. In thisLED lamp, the resin portion preferably has at least one side surface.The side surface is preferably separated from another surface that isable to reflect the outgoing light of the resin portion, preferablysurrounds the side surfaces of the LED chip and is preferably curved atleast partially.

[0016] In one preferred embodiment of the present invention, the LEDchip preferably has at least three planar side surfaces, each adjacentpair of which is preferably joined together by a corner portion.

[0017] In this particular preferred embodiment, at least part of theside surface of the resin portion, which faces the corner portion of theLED chip, is preferably curved.

[0018] More specifically, an angle defined by the curved part of theresin portion with respect to the center of the resin portion ispreferably greater than the largest possible angle of rotation of theLED chip being mounted onto the substrate. The angle of rotation ispreferably defined with respect to the center of the LED chip.

[0019] In another preferred embodiment, the resin portion preferably hasan axisymmetric shape.

[0020] In a specific preferred embodiment, the resin portion preferablyhas the shape of a cylinder, of which the diameter is longer than thediagonals of the LED chip.

[0021] In that case, the LED lamp is preferably designed so as tosatisfy 0.02 mm≦h≦0.1 mm and 0.15 mm≦x≦0.5 mm, where h is the distancebetween the upper surface of the resin portion including the phosphorand that of the LED chip and x is the distance between the side surfaceof the resin portion including the phosphor and those of the LED chip.

[0022] In another preferred embodiment, the phosphor is preferably anon-YAG-based substance, and if h exceeds 0.1 mm, then the LED lamppreferably satisfies 0.47≦h/x≦1.82, where h is the distance between theupper surface of the resin portion including the phosphor and that ofthe LED chip and x is the distance between the side surface of the resinportion including the phosphor and those of the LED chip.

[0023] In still another preferred embodiment, the resin portionincluding the phosphor is preferably made of a silicone resin. Thephosphor preferably has a mean particle size of 3 μm to 15 μm and agreater specific gravity than the silicone resin. The LED lamppreferably satisfies 0.2≦h/x≦0.5, where h is the distance between theupper surface of the resin portion including the phosphor and that ofthe LED chip and x is the distance between the side surface of the resinportion including the phosphor and those of the LED chip.

[0024] In this particular preferred embodiment, the resin portionincluding the phosphor preferably includes particles of a thixo agent,of which the mean particle size is less than 1 μm.

[0025] In yet another preferred embodiment, not only the LED chip butalso at least one more LED chip are preferably bonded to the substrate,and each of the LED chips is preferably covered with the resin portionseparately.

[0026] In that case, the LED lamp preferably further includes areflective member with reflective surfaces that are sloped so as toreflect the outgoing light of the resin portions of the LED chips awayfrom the substrate. The reflective surfaces are preferably sloped so asto surround the respective LED chips.

[0027] More particularly, the reflective member is preferably a platehaving multiple openings, each of which surrounds an associated one ofthe LED chips, and is preferably provided on the substrate. Thereflective member is preferably at most twenty times as thick as theresin portion.

[0028] In a specific preferred embodiment, the reflective memberpreferably has a thickness of at most 5 mm.

[0029] In yet another preferred embodiment, not only the LED chip butalso at least one more LED chip are preferably bonded to the substrate,and all of the LED chips are preferably covered with the single resinportion.

[0030] In yet another preferred embodiment, the LED lamp preferablyfurther includes a reflective member with a reflective surface that issloped so as to reflect the outgoing light of the resin portion awayfrom the substrate.

[0031] In this particular preferred embodiment, the reflective member ispreferably a plate provided on the substrate, and the reflective surfaceis preferably defined by the inner wall of an opening of the plate so asto surround the side surface of the resin portion including thephosphor.

[0032] In yet another preferred embodiment, the LED lamp preferablyfurther includes a second resin portion that covers the resinportion(s).

[0033] In yet another preferred embodiment, the LED lamp preferablyfurther includes a second resin portion that fills a gap between theside surface of the resin portion including the phosphor and thereflective member.

[0034] In a specific preferred embodiment, the second resin portionpreferably functions as a lens.

[0035] In yet another preferred embodiment, the center axis of the resinportion including the phosphor preferably substantially corresponds withthat of the LED chip.

[0036] A method for fabricating an LED lamp according to a preferredembodiment of the present invention preferably includes the steps of (a)preparing a substrate on which at least one LED chip has been flip-chipbonded and (b) providing a resin portion on the substrate. The resinportion preferably covers the LED chip and preferably includes aphosphor that transforms the emission of the LED chip into light havinga longer wavelength than the emission. In this method, the step (b)preferably includes the step of molding a resin material such that theresin portion has an exposed side surface.

[0037] The step (b) may include the steps of: (b1) molding the resinmaterial with a member that defines the shape of the side surface of theresin portion, thereby forming the resin portion; and (b2) removing themember from the side surface of the resin portion.

[0038] In one preferred embodiment of the present invention, the step(a) may include the step of preparing a substrate on which multiple LEDchips have been flip-chip bonded. In that case, the step (b) preferablyincludes the step of covering each of the LED chips with the resinportion separately.

[0039] In this particular preferred embodiment, the step (b) preferablyincludes the step of forming the resin portion in a cylindrical shape.

[0040] In another preferred embodiment, the method may further includethe step (c) of arranging a reflective member, having a reflectivesurface for reflecting the outgoing light of the resin portion, on thesubstrate after the step (b) has been performed.

[0041] In this particular preferred embodiment, the step (a) may includethe step of preparing a substrate on which multiple LED chips have beenflip-chip bonded. In that case, the step (c) preferably includes thestep of arranging a reflective member, having a plurality of reflectivesurfaces surrounding the LED chips, on the substrate.

[0042] In a specific preferred embodiment, the method preferably furtherincludes the step (d) of stacking a second resin portion on the resinportion including the phosphor after the step (c) has been performed.

[0043] In that case, the step (d) preferably includes the step offorming the second resin portion in a lens shape.

[0044] In an LED lamp according to a preferred embodiment of the presentinvention, the side surface of a resin portion, including a phosphor, isseparated from another surface that is able to reflect the outgoinglight of the resin portion, and surrounds the side surfaces of an LEDchip. Accordingly, any light ray being transmitted through the resinportion after having gone out of the LED chip through a side surfacethereof needs to go substantially the same distance, which hardlychanges with the direction of the light ray. As a result, the colorunevenness can be reduced significantly. Particularly when the resinportion is formed in a cylindrical shape, the color unevenness can bereduced even more effectively. In that case, even if the LED chips beingmounted face various directions, the color unevenness still hardlychanges with the direction.

[0045] Other features, elements, processes, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of preferred embodiments of the presentinvention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a cross-sectional view illustrating a conventional LEDlamp.

[0047]FIG. 2 is a cross-sectional view illustrating a portion of the LEDlamp shown in FIG. 1 on a larger scale.

[0048]FIGS. 3A and 3B are respectively a cross-sectional view and a planview schematically illustrating an LED lamp according to a firstspecific preferred embodiment of the present invention.

[0049]FIG. 4 is a perspective view showing an exemplary method offorming the resin portion shown in FIG. 3.

[0050]FIGS. 5A, 5B and 5C are perspective views showing other methods offorming the resin portion shown in FIG. 3.

[0051]FIGS. 6A and 6B are respectively a cross-sectional view and a planview schematically illustrating a main portion of the LED lamp of thefirst preferred embodiment.

[0052]FIG. 6C is a diagram showing the spatial distribution of luminousintensity of the LED lamp of the first preferred embodiment.

[0053]FIGS. 7A and 7B are respectively a cross-sectional view and a planview schematically illustrating a main portion of an LED lamp of acomparative example.

[0054]FIG. 7C is a diagram showing the spatial distribution of luminousintensity of the LED lamp of the comparative example.

[0055]FIGS. 8A and 8B are respectively a cross-sectional view and a planview schematically illustrating an LED lamp according to a secondspecific preferred embodiment of the present invention.

[0056]FIGS. 9A and 9B are respectively a cross-sectional view and a planview schematically illustrating an LED lamp according to a thirdspecific preferred embodiment of the present invention.

[0057]FIG. 10 is a plan view schematically illustrating an LED lampaccording to a fourth specific preferred embodiment of the presentinvention.

[0058]FIG. 11 is a cross-sectional view schematically illustrating anLED lamp according to a fifth specific preferred embodiment of thepresent invention.

[0059]FIG. 12 is a diagram showing the spatial distribution of luminousintensity of a flip-chip-bonded blue LED chip.

[0060]FIG. 13 is a cross-sectional view schematically illustrating anLED lamp according to a sixth specific preferred embodiment of thepresent invention.

[0061]FIG. 14 is a graph showing how the chromaticity difference changeswith x in the sixth preferred embodiment.

[0062]FIG. 15 is a perspective view schematically illustrating an LEDlamp according to a seventh specific preferred embodiment of the presentinvention.

[0063]FIG. 16 is an exploded perspective view of a card LED lamp.

[0064]FIG. 17 is a cross-sectional view illustrating a portion of thecard LED lamp shown in FIG. 16 including an LED chip.

[0065]FIGS. 18A and 18B are respectively a cross-sectional view and aplan view schematically illustrating an LED lamp according to an eighthspecific preferred embodiment of the present invention.

[0066]FIG. 19A is a plan view schematically illustrating a resin portionin an LED lamp according to a preferred embodiment of the presentinvention.

[0067]FIG. 19B is a plan view schematically illustrating a resin portionin an LED lamp of a comparative example.

[0068]FIG. 20 shows various dimensional parameters for an LED lampaccording to a preferred embodiment of the present invention.

[0069]FIGS. 21A and 21B show how to measure the spatial distribution ofluminous intensity of an LED lamp.

[0070]FIG. 22A is a graph showing the spatial distribution of acorrelated color temperature for a light ray with a peak wavelength of464 nm in an LED lamp according to a preferred embodiment of the presentinvention.

[0071]FIG. 22B is a graph showing the spatial distribution of acorrelated color temperature for a light ray with a peak wavelength of458 nm in the LED lamp of the preferred embodiment of the presentinvention.

[0072]FIG. 23 is a graph showing the difference in correlated colortemperature between the central and peripheral portions of an LED lampaccording to a preferred embodiment of the present invention.

[0073]FIGS. 24A and 24B are respectively a cross-sectional view and planview schematically illustrating a tapered first resin portion.

[0074]FIG. 25 is a cross-sectional view schematically illustrating asecond resin portion that functions as a lens array.

[0075]FIG. 26 is a cross-sectional view schematically illustrating theflow of a resin while the second resin portion is being formed.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0076] Hereinafter, preferred embodiments of the present invention willbe described with reference to the accompanying drawings. In thedrawings, a number of different members, appearing on multiple sheetsbut having substantially the same functions, are collectively identifiedby the same reference numeral for the sake of simplicity.

Embodiment 1

[0077] First, referring to FIGS. 3A and 3B, illustrated is an LED lampaccording to a first specific preferred embodiment of the presentinvention. As shown in FIGS. 3A and 3B, the LED lamp preferably includesa substrate 11, an LED chip 12 bonded to the substrate 11, and a resinportion 13 including a phosphor (or luminophore). In this preferredembodiment, the LED chip 12 is preferably flip-chip bonded to theprincipal surface of the substrate 11. Although not shown in FIG. 3A or3B, interconnects are actually provided on the substrate 11 andelectrically connected to the electrodes of the LED chip 12 mounted. TheLED chip 12 is preferably supplied with a predetermined current orvoltage from a lighting circuit (not shown) and through theinterconnects on the substrate 11 to make the LED chip 12 emit thelight.

[0078] The phosphor dispersed in the resin portion 13 absorbs, and isexcited by, the emission of the LED chip 12, thereby producingfluorescence. The light produced from the phosphor preferably has alonger wavelength than the emission of the LED chip 12. For example,when a blue LED chip is used as the LED chip 12, (Y.Sm)₃, (Al.Ga)₅O₁₂:Ceor (Y_(0.39)Gd_(0.57)Ce_(0.03)Sm_(0.01))₃Al₅O₁₂ can be used effectivelyas the phosphor. By using such a phosphor, part of the blue ray emittedfrom the LED chip 12 can be transformed into a yellow ray and theresultant illumination looks almost white overall.

[0079] Not just the phosphor but also particles of a thixo agent, ofwhich the mean particle size is smaller than 1 μm, are preferably addedto the resin portion 13. Examples of the thixo agents include fineparticles of silica, titania, alumina, and/or magnesium oxide. Thesefine particles have a mean particle size of several nanometers, which issmaller than that of the phosphor by approximately two orders ofmagnitude. The thixo agent contributes to maintaining the shape of theresin portion 13.

[0080] In this preferred embodiment, the resin portion 13 preferably hasa side surface, which is separated from another surface (not shown) thatcan reflect the outgoing light of the resin portion 13. Morespecifically, the resin portion 13 is preferably formed in a cylindricalshape so as to have a diameter longer than the diagonals of the LED chip12 and be higher than the LED chip 12. As shown in FIGS. 3A and 3B, theside surface of the resin portion 13 is preferably a curved surface thatsurrounds the side surfaces of the LED chip 12. As used herein, the“surface that can reflect the outgoing light of the resin portion 13” istypically a reflective surface of a reflective member that is providedspecially for the purpose of reflection but may also be a surface of anyother member.

[0081] In this manner, the side surface of the resin portion 13 of thispreferred embodiment is not defined by the reflective surface of areflective member, for example, but may be a freely designed curvedsurface. Thus, the color unevenness can be reduced effectively.

[0082] Hereinafter, a method of forming the cylindrical resin portion 13will be described with reference to FIG. 4.

[0083] First, a substrate 41 on which an LED chip 44 has been mounted ispreferably prepared. In this preferred embodiment, the LED chip 44 ispreferably flip-chip bonded to the principal surface of the substrate41. Next, a plate 42 with a cylindrical hole (opening) is brought intoclose contact with the principal surface of the substrate 41.Thereafter, a resin liquid including the phosphor is poured into thecylindrical hole. The plate 42 preferably has a thickness of 0.02 mm to1.1 mm. The diameter of the hole is preferably longer (e.g., about 0.8mm) than the diagonals (of 0.3 mm to 1.0 mm, for example) of the LEDchip 44.

[0084] After the resin liquid has been poured into the hole of the plate42, the excessive part of the resin liquid over the upper surface of theplate 42 is flattened with a squeeze 43 and then the resin liquid isthermally set. Thereafter, the plate 42 is removed from over thesubstrate 41, thereby obtaining a cylindrical resin portion thatentirely covers the LED chip 44.

[0085] In the example illustrated in FIG. 4, just one LED chip 44 ismounted on the substrate 41 and just one hole is provided through theplate 42. However, if multiple LED chips 44 are mounted on the substrate41, a plurality of cylindrical resin portions can be formed at the sametime by using a plate that has multiple holes for the respective LEDchips 44.

[0086] According to the method shown in FIG. 4, the resin portion thatencapsulates the LED chip 44 can be molded before a reflective member(or reflector) is attached onto the substrate 41. Thus, the shape of theresin portion can be freely determined without being limited by theshape of the reflective surface of the reflective member. Morespecifically, the hole shape of the plate 42 defines the side surfaceshape of the resin portion. Accordingly, by controlling the shape ofthis hole, the resin portion can be formed in any other shape, not justcylindrical. For example, if a triangular prism or rectangularparallelepiped hole is provided through the plate 42, the resin portioncan also be formed in a shape corresponding with that of the hole.

[0087] It should be noted that a “cross-sectional shape of a resinportion” is taken herein on a plane that is defined perpendicularly to anormal to the principal surface of the substrate. According to thisdefinition, the cylindrical resin portion has a “circular”cross-sectional shape. In this preferred embodiment, however, thecross-sectional shape of the resin portion does not have to be“completely round” in a strict sense. If the cross-sectional shape ofthe resin portion is a polygon with a relatively small number ofvertices such as a triangle or a rectangle, then some problems occur aswill be described later. In contrast, if the cross-sectional shape is apolygon with six or more vertices, then the polygon is sufficientlyaxisymmetric and can be regarded as substantially “circular”. This iswhy the “cylindrical resin portion” may also have a polygonalcross-sectional shape with six or more vertices.

[0088] Also, examples of “resins” include herein thermoplastic resins,thermosetting resins, resins that cure upon the exposure to a radiationsuch as an ultraviolet ray, inorganic polymers, and glasses. Optionally,the resin may further include an additive such as a photostabilizer.

[0089] In the preferred embodiment described above, the side surface ofthe resin portion is curved entirely. However, the effects of thepresent invention are also achievable even if the side surface is curvedjust partially. This point will be described with reference to FIGS. 19Aand 19B.

[0090]FIG. 19A is a plan view illustrating an exemplary layout of theresin portion 13 and the LED chip 12 surrounded with the resin portion13. In FIG. 19A, the LED chip 12 that has not rotated from theoriginally intended position is indicated by the dotted square, whilethe LED chip 12 that has rotated and shifted from the original positionis indicated by the solid square. The angle of shift caused by therotation is supposed herein to be at most equal to α degrees. The resinportion 13 shown in FIG. 19A has four curved corners 13 a. The largestpossible angle defined by any of these four curved corners 13 a withrespect to the center of the resin portion 13 is supposed herein to beequal to 2×α degrees. In that case, as can be seen from FIG. 19A, if theangle of shift caused by the rotation is smaller than a degrees, thenthe extended diagonals on the upper surface of the LED chip 12 alwayscross the curved portions 13 a of the side surface of the resin portion13, not the flat portions thereof. For example, one of the two diagonalsof the LED chip 12 that has not shifted at all from its originalposition is identified by G1, while the associated diagonal of the LEDchip 12 that has rotated α degrees from its original position isidentified by G2. Take a look at the light rays that have gone out ofthe LED chip 12 through a side surface thereof and along the diagonalsG1 and G2. As shown in FIG. 19A, the distance that the outgoing lightray of the LED chip 12 at the original position should go along thediagonal G1 to reach the side surface of the resin portion 13 is notsignificantly different from the distance that the outgoing light ray ofthe LED chip 12 at the shifted position should go along the diagonal G2to reach the side surface of the resin portion 13. This is because theside surface of the resin portion 13 has the curved corners 13 a at thepositions shown in FIG. 19A.

[0091] In contrast, the resin portion 13 shown in FIG. 19B has no curvedcorners. Accordingly, the distance that the outgoing light ray of theLED chip 12 at the original position should go along the diagonal G1 toreach the side surface of the resin portion 13 is significantlydifferent from the distance that the outgoing light ray of the LED chip12 at the shifted position should go along the diagonal G2 to reach theside surface of the resin portion 13. When these distances aresignificantly different from each other, color unevenness is easilycaused as a result of the rotation of the LED chip 12.

[0092] As can be understood easily from the foregoing description, notthe entire side surface of the resin portion 13 has to be a curvedsurface that surrounds the side surfaces of the LED chip. That is tosay, the curved surfaces of the resin portion need to be present so asto face at least the corners of the LED chip. More specifically, theangle (=2α) defined by any of the curved surfaces 13 a of the resinportion 13 with respect to the center of the resin portion 13 is atleast greater than the largest possible angle of rotation of the LEDchip 12 being mounted onto the substrate.

[0093] When the side surface of the resin portion has such curvedsurfaces, the thickness of the resin portion as measured laterally(i.e., parallel to the principal surface of the substrate) is notuniform. If a thin phosphor layer is applied or deposited on thesurfaces of the LED chip, then the phosphor layer will have asubstantially uniform thickness on the surfaces of the LED chip. Thus,the resin portion for use in preferred embodiments of the presentinvention has a unique shape, which is quite different from that of thephosphor layer.

[0094] Next, a cross-sectional shape of the resin portion 13 taken on aplane that crosses the substrate 11 at right angles will be described.The right and left sides of this cross section do not have to beperpendicular to the substrate 11. Instead, according to the methodshown in FIG. 4, the resin portion 13 may also be formed as to haveslightly tapered sides. FIGS. 24A and 24B show a cross-sectional shapeand a planar shape of such a tapered resin portion, respectively. InFIG. 24A, the ratio of the top diameter L2 to the bottom diameter L1(which will be referred to herein as the “L2/L1 ratio”) is preferably atleast 0.5. This is because the inner walls of the hole of the platepreferably stand substantially perpendicularly to the principal surfaceof the substrate in order to pour the resin liquid into the hole with nogaps left. Also, if the top diameter L2 is too small, then the colorunevenness caused by the shift of the LED chip will have seriouseffects. Thus, the L2/L1 ratio is preferably as close to one aspossible.

[0095] In the method of forming the resin portion described above, theupper surface of the resin portion is smoothed out with the squeeze 43.Thus, the upper surface of the resin portion does not become excessivelyuneven but substantially flat. While the resin liquid is being cured,the upper surface of the resin portion may lose its planarity to acertain degree but never becomes rugged enough to cause perceivablecolor unevenness. In addition, since the resin portion is cylindrical,the upper surface of the resin portion has a relatively small area.Accordingly, even if the upper surface of the resin portion has lostmuch of its planarity, almost no color unevenness will be noticeable inthat case. It should be noted that the cylindrical resin portion for usein various preferred embodiments of the present invention cannot beformed by the conventional method in which the resin liquid is pouredinto, and then cured in, the cup reflector.

[0096] Hereinafter, other methods of forming the resin portion will bedescribed with reference to FIGS. 5A through 5C.

[0097] First, referring to FIG. 5A, a mold 45 that defines the shape ofthe resin portion 13 is preferably prepared and filled with the resinliquid according to an alternative method. Thereafter, the resin liquidis somewhat cured with a heat source or an additive that increases itsviscosity. Then, the mold 45 including the half-cured resin portion isplaced on the substrate 41, thereby transferring the resin portion ontothe substrate 41. Finally, the mold 45 is removed from over thesubstrate 41 and the resin portion that has been transferred onto thesubstrate 41 is further cured.

[0098] According to another alternative method shown in FIG. 5B, thehalf-cured resin portion 13 may be picked out of the mold 45, pressedagainst the LED chip 44 that has been mounted on the substrate 41, andthen further cured.

[0099] Optionally, a method that uses no mold 45 may also be adopted asshown in FIG. 5C. Specifically, in the example illustrated in FIG. 5C,first, the surface of the substrate 41 on which the LED chip 44 has beenmounted is coated with a photosensitive resin layer 46. Thephotosensitive resin layer 46 may be obtained by applying a photoresist,including a phosphor, onto the substrate 41, for example. Next, only aselected area of the photosensitive resin layer 46 is exposed toradiation and developed through a photomask 48 that has an opaquepattern 47 defining the planar shape of the resin portion, therebyforming the resin portion. It should be noted that the photosensitiveresin layer 46 may be made of either a negative photoresist or apositive photoresist as long as the opaque pattern 47 of the photomask48 has an appropriately selected shape.

[0100] As described above, in this preferred embodiment, the LED chip isfixed onto the substrate by a flip-chip bonding technique. Such aflip-chip bonding process may be carried out in the following manner.First, the LED chip is sucked with a collet or any other suitableinstrument and arranged at an appropriate location on the substrate.Thereafter, the LED chip is preferably bonded onto the substrate byultrasonic flip-chip bonding or any of various other techniques. In theultrasonic flip-chip bonding technique, the LED chip is subjected toultrasonic vibrations while the metal electrodes on the LED chip arepressed against the metal electrodes on the substrate, thereby weldingand bonding the two groups of metal electrodes together. The ultrasonicflip-chip bonding can be used effectively to mount and arrange aplurality of LED chips at a high density, because this technique needsno solder for connection and can be carried out at a relatively lowtemperature. According to the ultrasonic flip-chip bonding process,however, the LED chips easily rotate under the ultrasonic vibrations andface various directions before welded and bonded to the substratecompletely.

[0101] Accordingly, if the resin portion including the phosphor has asquare cross-sectional shape, then the distance that the outgoing lightray of the LED chip should go to pass through the resin portion changessignificantly with the direction thereof. As a result, the degree ofcolor unevenness perceived changes depending on the direction that theLED chip faces relative to the resin portion.

[0102] Hereinafter, it will be described with reference to FIGS. 6Athrough 6C and FIGS. 7A through 7C how the spatial distribution ofluminous intensity of the LED chip is affected by the cross-sectionalshape of the resin portion.

[0103]FIGS. 6A and 6B are respectively a cross-sectional view and a planview schematically illustrating a main portion of the LED lamp of thefirst preferred embodiment. On the other hand, FIGS. 7A and 7B arerespectively a cross-sectional view and a plan view schematicallyillustrating a main portion of an LED lamp of a comparative example, ofwhich the resin portion including the phosphor is formed in aquadrangular prism shape.

[0104] In FIG. 6B, two planes L1 and S1 are defined perpendicularly tothe principal surface of the substrate 11. In the same way, two planesL2 and S2 are also defined perpendicularly to the principal surface ofthe substrate 11. FIG. 6C shows the spatial distribution of luminousintensity on the L1 and S1 planes, which are also identified by thecommon reference signs L1 and S1, respectively. Likewise, FIG. 7C showsthe spatial distribution of luminous intensity on the L2 and S2 planes,which are also identified by the common reference signs L2 and S2,respectively. In this case, the spatial distribution of luminousintensity is obtained by calculating the luminous intensities for a −90degree to 90 degree range, which is defined with respect to a normal tothe principal surface of the substrate, through computer simulations.That is to say, this 180 degree range is defined with the normalregarded as representing the 0 degree direction.

[0105] As can be seen from FIG. 6C, if the resin portion 13 has acircular cross section, almost the same spatial distribution of luminousintensities are obtained on the L1 and S1 planes. In contrast, if theresin portion 13 has a rectangular cross section, then the spatialdistribution of luminous intensity on the L2 plane will be significantlydifferent from that on the S2 plane as can be seen from FIG. 7C.

[0106] Thus, when the resin portion 13 has a square cross section, thespatial distribution of luminous intensity is changeable with thedirection, and the resultant color unevenness is quite perceivable. Inthat case, the color unevenness cannot be reduced unless the directionof the LED chip 12 with respect to the resin portion 13 is controlledappropriately. However, according to the ultrasonic flip-chip bondingtechnique, the direction of the LED chip 12 is non-controllable asdescribed above.

[0107] In contrast, if the resin portion 13 has a circular cross sectionas in the preferred embodiment described above, then the directiondependence of the spatial distribution of luminous intensity can bereduced significantly and the direction-dependent color unevennessproblem can be resolved. It should be noted that this particular effectof the present invention is also achievable to a certain extent even ifthe resin portion 13 does not have a circular cross section but anelliptical cross section, for example. Even so, however, the center axisof the resin portion including the phosphor preferably substantiallycorresponds with that of the LED chip.

Embodiment 2

[0108] Hereinafter, an LED lamp according to a second specific preferredembodiment of the present invention will be described with reference toFIGS. 8A and 8B. FIGS. 8A and 8B are respectively a cross-sectional viewand a plan view schematically illustrating the LED lamp of the secondpreferred embodiment.

[0109] The LED lamp of the second preferred embodiment preferablyincludes a substrate 11, an LED chip 12 that has been bonded to thesubstrate 11, a resin portion 13 including a phosphor, and a reflector51 that has been attached to the substrate 11. All of these members ofthe LED lamp, except the reflector 51, are the same as the counterpartsof the first preferred embodiment described above, and the descriptionthereof will be omitted herein.

[0110] As shown in FIG. 8A, the reflector 51 preferably has a downwardlytapered reflective surface, which is axisymmetric with respect to thecenter of the LED chip 12. This reflective surface is preferably theside surface of an opening of the metallic reflector 51. The shortestdiameter of this opening (i.e., as measured closest to the substrate, orat the bottom of the opening) is longer than the diameter of thecylindrical resin portion 13. Accordingly, the reflector 51 may alsohave a parabolic shape.

[0111] The reflective surface of the reflector 51 receives a light ray52, which has been emitted from the LED chip 12 through a side surfacethereof, and reflects the light ray 52 substantially perpendicularly tothe principal surface of the substrate 11 as shown in FIG. 8A. Thus, theoptical output of this LED lamp as measured perpendicularly to theprincipal surface of the substrate is higher than that of the LED lampincluding no reflector 51.

[0112] In the LED lamp of this preferred embodiment, a gap of at least0.1 mm is preferably provided between the reflective surface and theside surface (i.e., the outer surface) of the resin portion 13. For thatreason, the light ray is not reflected back from the reflective surfaceto the resin portion 13 so easily. As a result, the color unevenness,which might be caused due to the optical path difference in thesituation shown in FIG. 2, is hardly noticeable if any.

Embodiment 3

[0113] Hereinafter, an LED lamp according to a third specific preferredembodiment of the present invention will be described with reference toFIGS. 9A and 9B. FIGS. 9A and 9B are respectively a cross-sectional viewand a plan view schematically illustrating the LED lamp of the thirdpreferred embodiment.

[0114] In this preferred embodiment, a second resin portion 61 ispreferably further provided over the substrate 11 so as to cover thecylindrical resin portion 13. Also, this second resin portion 61 ispreferably shaped so as to function as a lens. Specifically, this secondresin portion 61 preferably transforms light rays 62, which have beenemitted from the LED chip 12 through upper and side surfaces thereof,into substantially parallel light rays. As a result, the optical outputof the LED lamp increases as measured perpendicularly to the principalsurface of the substrate.

[0115] The second resin portion 61 of this preferred embodiment ispreferably made of an epoxy resin, for example, and includes nophosphor. In this preferred embodiment, the second resin portion 61preferably covers the first resin portion 13 entirely and fills the gapbetween the reflective surface of the reflector 51 and the side surfaceof the first resin portion 13. The second resin portion 61 also performsthe functions of protecting the first resin portion 13 and increasingthe reliability thereof. The second resin portion 61 with thesefunctions is in close contact with the reflective surface but includesno phosphor, thus hardly causing the color unevenness problem shown inFIG. 2.

[0116] In the preferred embodiment illustrated in FIG. 9A, the secondresin portion 61 is formed in a lens shape. However, the second resinportion 61 may also have any of various other shapes as long as thesecond resin portion 61 can perform the desired optical functions.

[0117]FIGS. 8A and 8B or 9A and 9B illustrate only one LED chip 12. Inan actual LED lamp, however, a number of LED chips are preferablyarranged on the same substrate. In that case, the reflector 51preferably has a plurality of openings that surrounds the respective LEDchips. Each of those openings of the reflector 51 also preferably has asloped side surface functioning as a reflective surface.

[0118] The reflector 51 is preferably at most twenty times as thick asthe resin portion 13 including the phosphor. To reduce the thickness ofthe LED lamp sufficiently, the reflector 51 preferably has a thicknessof 5 mm or less.

[0119] In this preferred embodiment, the shape and sizes of thereflective surface are defined so as to surround its associated LEDchip. Thus, the reflector 51 can have a reduced thickness and theoverall LED lamp can also have a reduced size.

[0120] It should be noted that if a number of LED chips are arranged onthe same substrate, a reflector with multiple reflective surfacessurrounding the respective LED chips is preferably attached to thesubstrate and then a second resin portion, functioning as a lens array,is preferably provided thereon as shown in FIG. 25. This second resinportion does not have to be divided into multiple lenses for therespective LED chips but may be a single continuous member as shown inFIG. 25. In that case, the second resin portion has junction portionsthat link the array of lens together. Those junction portions mayfunction as optical waveguides. Accordingly, the second resin portioncan mix together the light rays that have been emitted from therespective LED chips and first resin portion, thus further reducing thecolor unevenness.

[0121] The substrate 11 and reflector 51 are originally two separatemembers. Accordingly, a gap 101 may be intentionally provided betweenthe substrate 11 and the reflector 51 as shown in FIG. 26. By providingsuch a gap 101, a portion of the second resin may flow along the pathindicated by the arrow 102 in FIG. 26 into the gap 101 while the secondresin portion is being formed. When such a configuration is adopted,bubbles, created in the second resin portion being formed over thereflector 51, can flow into the gap 101 along with the second resin. Asa result, most of the bubbles can be removed from the parts of thesecond resin portion that cover the LED chips.

[0122] In the preferred embodiment described above, light can beextracted efficiently from the respective LED chips. However, if themultiple LED chips were surrounded with a single reflective surface,then a light ray emitted from one of those LED chips should be absorbedinto adjacent LED chips and the emission could not be extractedefficiently enough. Also, in that case, the light ray emitted from eachLED chip should go a long distance to reach the reflective surface.Thus, the reflective surface should have its height increased. This isnot preferable to reduce the size of the LED lamp.

Embodiment 4

[0123] Hereinafter, an LED lamp according to a fourth specific preferredembodiment of the present invention will be described with reference toFIG. 10. FIG. 10 is a plan view schematically illustrating the LED lampof the fourth preferred embodiment.

[0124] In this preferred embodiment, a number of LED chips 12 are bondedto the same substrate 11 by the ultrasonic flip-chip bonding techniquedescribed above. Accordingly, while being mounted on the substrate 11,the LED chips 12 rotate and face various directions as shown in FIG. 10.It should be noted that the difference in the angle of rotation betweenthe respective LED chips 12 is exaggerated and greater than the actualone.

[0125] According to this preferred embodiment, even though therespective LED chips 12 face various directions as shown in FIG. 10, theeffects of the color unevenness can also be reduced because the resinportions 13 are formed in a cylindrical shape.

Embodiment 5

[0126] Hereinafter, an LED lamp according to a fifth specific preferredembodiment of the present invention will be described with reference toFIG. 11. FIG. 11 is a cross-sectional view schematically illustratingthe LED lamp of the fifth preferred embodiment.

[0127] The LED lamp of this preferred embodiment preferably satisfies b0.2≦h/x≦0.5, where h is the distance between the upper surface of theresin portion 13 including the phosphor and that of the LED chip 12 andx is the distance between the side surface of the resin portion 13 andthose of the LED chip 12.

[0128]FIG. 12 shows the spatial distribution of luminous intensity of aflip-chip-bonded blue LED chip. In FIG. 12, the curve 81 represents thespatial distribution of luminous intensity of the LED chip, while thecurve 82 represents the spatial distribution of luminous intensity of anormal light source in accordance with the cosine emission law. As canbe seen from FIG. 12, the luminous intensity of the flip-chip bonded LEDchip as measured perpendicularly to the principal surface of thesubstrate is approximately 20% lower than that of the normal lightsource. This is believed to be because the quantity of the light emittedfrom the upper surface of the LED chip would be about 20% smaller thanthat of the light emitted from the side surfaces of the LED chip.Accordingly, the spatial distribution of luminous intensity cannot beimproved if a part of the resin portion including the phosphor, throughwhich the light that has been emitted from the side surfaces of the LEDchip passes, is as thick as another part of the resin portion, throughwhich the light that has been emitted from the upper surface of the LEDchip passes.

[0129] Thus, to compensate for the difference between the quantity ofthe light emitted from the upper surface of the LED chip 12 and that ofthe light emitted from the side surfaces thereof, that part of the resinportion 13, located over the upper surface of the LED chip 12, is maderelatively thin in this preferred embodiment. It should be noted thatthe first resin portion 13 is illustrated as an excessively thick one inFIG. 11 for the sake of clarity.

[0130] The present inventors discovered and confirmed via experimentsthat where the phosphor was included in those parts of the resin portion13, located over the upper surface of the LED chip and around the sidesurfaces of the LED chip, under the same condition, the spatialdistribution of luminous intensity could be improved when 0.2≦h/x≦0.5was satisfied. That is to say, if the resin portion 13 is shaped so asto satisfy this inequality, the resultant spatial distribution ofluminous intensity will be substantially represented by the curve 82shown in FIG. 12.

[0131] In this preferred embodiment, the resin portion 13 has acylindrical shape, while the LED chip 12 has a rectangularparallelepiped shape. Accordingly, the thickness (i.e., the lateralsize) of the resin portion 13 that covers the side surfaces of the LEDchip 12 changes according to the direction. Thus, the “distance xbetween the side surface of the resin portion 13 and the side surfacesof the LED chip 12” means herein “the distance from the center of eachside surface of the LED chip 12 to the intersection between the sidesurface of the resin portion 13 and a line extending from that centerperpendicularly to the side surface of the resin portion 13”.

Embodiment 6

[0132] Hereinafter, an LED lamp according to a sixth specific preferredembodiment of the present invention will be described with reference toFIG. 13. FIG. 13 is a cross-sectional view schematically illustratingthe LED lamp of the sixth preferred embodiment.

[0133] If the phosphor is distributed non-uniformly in the cylindricalresin portion 13 (i.e., if the phosphor over the upper surface of theLED chip 12 is distributed differently from that around the sidesurfaces of the LED chip 12), then the resultant spatial distribution ofluminous intensity might deteriorate due to the non-uniform distributionof the phosphor. In view of this potential problem, this preferredembodiment provides a means for minimizing such deterioration.

[0134] The resin portion 13 including the phosphor is preferably made ofan epoxy resin or a silicone resin. While setting thermally, each ofthese resins has an extremely decreased viscosity albeit temporarily.Accordingly, if the phosphor has a mean particle size of 3 μm to 15 μmand has a greater specific gravity than the resin, then the phosphorwill cause a sedimentation phenomenon while the resin is settingthermally. FIG. 13 schematically illustrates a state in which such aphenomenon has occurred. In the exaggerated example shown in FIG. 13, asediment phosphor layer 101 is formed on the bottom of the resin layer102. However, the phosphor is normally not separated from the resin ascompletely as shown in FIG. 13. Also, by adding a thixo agent, thesedimentation of the phosphor during the thermal setting of the resincan be reduced to a certain degree.

[0135] Generally speaking, while setting thermally, the silicone resindoes not decrease its viscosity as extremely as the epoxy resin, issofter than the epoxy resin, and can relax the stress better than theepoxy resin. Accordingly, the silicone resin is preferred to the epoxyresin as a material for the resin portion 13. Thus, the presentinventors defined the conditions for matching the color of the light 103emitted from the upper surface of the resin portion 13 with that of thelight 104 emitted from the side surface of the resin portion 13 wherethe resin portion 13 was made of a silicone resin.

[0136] In this preferred embodiment, the distance between the uppersurface of the resin portion 13 including the phosphor and that of theLED chip 12 is also identified by h and the distance between the sidesurface of the resin portion 13 and those of the LED chip 12 is alsoidentified by x. The LED chip 12 was 0.3 mm square and had a thicknessof 0.09 mm. The distance h was set to 0.02 mm or 0.1 mm. When thedistance h was 0.02 mm, the distance x was selected from the six valuesof 0.1 mm, 0.15 mm, 0.2 mm, 0.25 mm, 0.3 mm and 0.35 mm. On the otherhand, when the distance h was 0.1 mm, the distance x was selected fromthe five values of 0.1 mm, 0.2 mm, 0.3 mm, 0.4 mm and 0.55 mm. Thephosphor exhibited a broad spectral distribution with a peak wavelengthof 575 nm. The phosphor and the silicone resin were mixed together at aweight ratio of approximately 70 to 30. The mixing and defoamingprocesses were carried out sufficiently with a machine.

[0137] With a current of about 40 mA supplied to the LED chip 12, thespectral irradiance of the light emitted from the upper surface of theresin portion 13 and that of the light emitted from the side surfacethereof were measured. The chromaticities of the illuminations wereobtained based on the results of this measurement. And the differenceΔCu′ v′ in chromaticity between the light emitted from the upper surfaceand the light emitted from the side surface was calculated.

[0138]FIG. 14 is a graph showing how the chromaticity difference ΔCu′ v′changed with x. In FIG. 14, the curve plotted with ▴ represents the dataobtained when h was 0.02 mm while the curve plotted with  representsthe data obtained when h was 0.1 mm.

[0139] As can be seen from the results shown in FIG. 14, when h was 0.02mm, the inflection point, at which the chromaticity difference startedto decrease, was located where x=0.15 mm. On the other hand, when h was0.1 mm, the inflection point, at which the chromaticity differencestarted to decrease, was located where x=0.2 mm. Thus, it can be seenthat if the distance h between the upper surface of the LED chip 12 andthat of the resin portion 13 is in the range of 0.02 mm to 0.1 mm, thecolor unevenness can be reduced by defining the distance x between theside surfaces of the LED chip 12 and the side surface of the cylindricalresin portion 13 within the range of 0.15 mm to 0.5 mm.

[0140] These data were obtained when h was 0.02 mm and when h was 0.1mm. By reducing the weight ratio or the concentration of the phosphorincluded in the resin portion, the resin portion can be thickened. Ifthe phosphor has a high weight ratio, then even a thin resin portion canabsorb a good portion of the light emitted from the LED chip and cantransform it into light with a longer wavelength. The properties of arelatively thick resin portion (in which h was greater than 0.1 mm)obtained by adding a non-YAG-based phosphor to a silicone resin wereevaluated.

[0141] Hereinafter, the results of the evaluation will be described indetail with reference to the accompanying drawings.

[0142] The phosphor and the silicone resin were mixed together at aweight ratio of approximately 70 to 30. The LED chip used had asubstantially rectangular parallelepiped shape with a height of 0.1 mmand an approximately square cross section of 0.32 mm×0.30 mm. Two typesof LED chips with a peak wavelength of 458 nm and a peak wavelength of464 nm were used.

[0143]FIG. 20 shows various dimensional parameters for a cylindricalresin portion that was formed so as to cover a single LED chip. In theexample shown in FIG. 20, the diameter and the height of the resinportion are identified by φ and H, respectively.

[0144] The spectral and spatial distribution was measured as shown inFIG. 21A and 21B. More specifically, the angular dependences of twoemission spectra were obtained with respect to two planes that weredefined perpendicularly to the principal surface of the substrate asshown in FIG. 21A The measurement was carried out with aspectrophotometer MCPD 1000 produced by Otsuka Electronics Co., Ltd. andwith a current of about 40 mA supplied to the LED chip for emissionpurposes.

[0145]FIG. 22A shows the data obtained about the light with a peakwavelength of 464 nm, i.e., the angular dependences for resin portionswith diameters φ of 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm and 1.0 mmand a height H of about 0.34 mm. FIG. 22B shows the data obtained aboutthe light with a peak wavelength of 458 nm in a similar manner. In FIGS.22A and 22B, the ordinate represents the correlated color temperature,while the abscissa represents the angle that is defined by a lineconnecting the center of the LED chip to that of the light receivingarea of a photodetector with respect to a normal to the principalsurface of the substrate as shown in FIG. 21 B.

[0146] As can be seen from FIGS. 22A and 22B, if the resin portion had adiameter φ of 0.7 mm or more, the correlated color temperature exhibitedlittle angular dependence, thus resulting in small color unevenness.

[0147] The data shown in FIGS. 22A and 22B were obtained by measuringthe quantities of the emission of the LED chip in fourteen differentdirections. Next, based on these data collected, the difference betweenthe data obtained at a zero degree (i.e., perpendicularly to thesubstrate) and the data obtained at a non-zero degree (i.e., with a tiltangle defined with respect to a normal to the substrate) was obtained.The former data will be referred to herein as “central data”, while thelatter data will be referred to herein as “peripheral data”. FIG. 23 isa graph showing how the difference between the central and peripheraldata (plotted as the ordinate) changes with the diameter φ of the resinportion (plotted as the abscissa). In FIG. 23, the curve plotted with represents the data about the light with a wavelength of 464 nm, whilethe curve plotted with ▴ represents the data about the light with awavelength of 458 nm.

[0148] As can be seen from FIG. 23, the difference between thecorrelated color temperatures (i.e., the difference between the centraland peripheral data) tended to increase not only when the resin portionhad a diameter of 0.6 mm or less but also when the resin portion had adiameter of 1.0 mm. Thus, it can be understood that the performance ofthe LED lamp also deteriorates if the resin portion has an excessivediameter φ.

[0149] The present inventors discovered and confirmed via experimentsthat if the cylindrical resin portion had a height H of 0.25 mm to 0.40mm and a diameter φ of 0.65 mm to 0.95 mm, then the color unevennesscould be minimized.

[0150] These preferred values are changeable if the sizes of the LEDchip are different from those of the LED chip that was used in theexperiments. Thus, the preferred range may also be defined by moreimportant parameters h and x shown in FIG. 11. In that case, the h/xratio was preferably in the range of 0.47 to 1.82, more preferably 0.60to 1.68, even more preferably 0.76 to 1.46, and most preferably 0.9 to1.26.

[0151] As shown in FIG. 19, even if the LED chip has rotated, the sidesurfaces of the LED chip should be fully covered with the resin portion.In view of this consideration, x is preferably at least equal to about0.02 mm. Once x is determined, h needs to be defined such that the h/xratio falls within one of the preferred ranges described above.

[0152] If an LED chip with a square upper surface is fully covered witha cylindrical resin portion having a diameter φ, then the diameter φneeds to be longer than the diagonals of the square. When the diameter φis equal to the diagonals, x is equal to (φ−φ/2^(1/2))/2. Accordingly,the inequality x>(φ−φ/2^(1/2))/2 is preferably satisfied.

Embodiment 7

[0153] Hereinafter, an LED lamp according to a seventh specificpreferred embodiment of the present invention will be described withreference to FIG. 15. FIG. 15 is a perspective view illustrating a cardLED lamp 121 according to this preferred embodiment, a connector 123to/from which the LED lamp 121 is attachable and removable, and alighting circuit 132 to be electrically connected to the LED lamp 121 byway of the connector 123.

[0154] As shown in FIG. 15, the card LED lamp 121 is preferably insertedinto the connector 123 through a pair of guide grooves 122. The guidegrooves 122 are provided to slide the edges of the substrate of the LEDlamp 121 in a predetermined direction while the LED lamp 121 is beinginserted into, or removed from, the connector 123. The connector 123includes a feeder electrode (not shown) to be electrically connected tothe feeder electrode (not shown) of the card LED lamp 121, and isconnected to the lighting circuit 132 via lines 131.

[0155] The LED lamp 121 includes a plurality of LED chips, which arepreferably bonded to a rectangular substrate. Each of those LED chips ispreferably covered with the cylindrical resin portion. Optionally, thesubstrate of the LED lamp 121 may have a multilevel interconnectstructure for connecting the respective LED chips to the feederelectrode. Also, a metallic reflector with multiple openings for therespective LED chips may be attached to the surface of the substrate.

[0156] In this manner, the LED lamp 121 of this preferred embodiment hasa card shape, which is similar to a memory card, for example, and can beattached into, or removed from, any of various types of appliances witha connector. Accordingly, even when the LED lamp 121 that has been usedin an illumination unit runs out of its life, the illumination unit canbe used continuously by replacing the exhausted LED lamp 121 with abrand-new LED lamp of the same shape. Also, if multiple types of LEDlamps 121 with mutually different properties are appropriately selectedand fitted in an illumination unit one after another, various types ofillumination can be provided with the same illumination unit.

[0157] Next, the configuration of the card LED lamp 121 of thispreferred embodiment will be described in further detail with referenceto FIGS. 16 and 17. FIG. 16 is an exploded perspective view of the cardLED lamp 121. FIG. 17 is a cross-sectional view illustrating a portionof the card LED lamp 121 including an LED chip.

[0158] Referring to FIG. 16, the LED lamp 121 of this preferredembodiment preferably includes a plurality of cylindrical resin portions213, which are arranged in matrix on a substrate 11. Although not shownin FIG. 16, each of the resin portions 213 includes an LED chip that hasbeen molded with the resin. As described above, a phosphor is preferablydispersed in the cylindrical resin portion 213 to transform the emissionof the LED chip into light with a longer wavelength.

[0159] A reflector 152 with multiple openings surrounding the respectivecylindrical resin portions 213 is preferably attached to the surface(i.e., the mount-side surface) of the substrate 11. The inside surfaceof each opening of the reflector 152 is downwardly tapered so as tofunction as a reflective surface for reflecting the emission of thecylindrical resin portion 213.

[0160] Next, referring to FIG. 17, each LED chip 153 of this preferredembodiment is preferably flip-chip bonded to an interconnect pattern 159of a multilayer wiring board 151, which is attached to a metal plate150. In this case, the metal plate 150 and the multilayer wiring board151 together make up the substrate 11. The LED chip 153 is covered withthe cylindrical resin portion 213 including the phosphor. And this resinportion (i.e., first resin portion) 213 is further covered with a secondresin portion 162 functioning as a lens.

[0161] In this preferred embodiment, the multilayer wiring board 151includes a two-layered interconnect pattern 159, in which interconnectsbelonging to the two different layers are connected together by way ofvia metals 163. Specifically, the interconnects belonging to the upperlayer are connected to the electrodes of the LED chip 153 via Au bumps161. The interconnect pattern 159 may be made of copper, nickel,aluminum, or an alloy mainly composed of these metals, for example.

[0162] The upper surface of the multilayer wiring board 151 having sucha configuration is mostly covered with the reflector 152 but ispartially exposed. A number of feeder electrodes (not shown) areprovided on the exposed areas of the multilayer wiring board 151. Thesefeeder electrodes are electrically connected to the lighting circuit ofan illumination unit by way of the connector into which the card LEDlamp is inserted.

[0163] In the example illustrated in FIG. 17, an underfill (stressrelaxing) layer 160 is preferably provided between the reflector 152 andthe multilayer wiring board 151. This underfill layer 160 can not onlyrelax the stress, resulting from the difference in thermal expansioncoefficient between the metallic reflector 152 and the multilayer wiringboard 151, but also ensure electrical insulation between the reflector152 and the upper-level interconnects of the multilayer wiring board151.

Embodiment 8

[0164] Hereinafter, an LED lamp according to an eighth specificpreferred embodiment of the present invention will be described withreference to FIGS. 18A and 18B. FIGS. 18A and 18B are respectively across-sectional view and a plan view schematically illustrating an LEDlamp according to the eighth preferred embodiment.

[0165] In this preferred embodiment, two LED chips 141 and 142 arebonded to the same substrate 11 and are covered with the samecylindrical resin portion 13 including the phosphor.

[0166] A portion of the light that has been emitted from each of theseLED chips 141 and 142 is transformed by the cylindrical resin portion 13into light having a longer wavelength. In this manner, even if multipleLED chips are covered with a single cylindrical resin portion, the colorunevenness can also be reduced.

[0167] It should be noted that the wavelength of the light emitted fromthe LED chip 141 does not have to be equal to that of the light emittedfrom the LED chip 142.

[0168] The present invention is effectively applicable for use invarious types of illumination sources that can replace the conventionalillumination sources utilizing electric discharge.

[0169] While the present invention has been described with respect topreferred embodiments thereof, it will be apparent to those skilled inthe art that the disclosed invention may be modified in numerous waysand may assume many embodiments other than those specifically describedabove. Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

What is claimed is:
 1. An LED lamp comprising: a substrate; an LED chip,which is flip-chip bonded to the substrate; and a resin portion, whichcovers the LED chip and which includes at least one type of phosphorthat transforms the emission of the LED chip into light having a longerwavelength than the emission, wherein the resin portion has at least oneside surface, which is separated from another surface that is able toreflect the outgoing light of the resin portion, which surrounds theside surfaces of the LED chip and at least part of which is curved. 2.The LED lamp of claim 1, wherein the LED chip has at least three planarside surfaces, each adjacent pair of which is joined together by acorner portion.
 3. The LED lamp of claim 2, wherein at least part of theside surface of the resin portion, which faces the corner portion of theLED chip, is curved.
 4. The LED lamp of claim 3, wherein an angledefined by the curved part of the resin portion with respect to thecenter of the resin portion is greater than the largest possible angleof rotation of the LED chip being mounted onto the substrate, the angleof rotation being defined with respect to the center of the LED chip. 5.The LED lamp of claim 1, wherein the resin portion has an axisymmetricshape.
 6. The LED lamp of claim 5, wherein the resin portion has theshape of a cylinder, of which the diameter is longer than the diagonalsof the LED chip.
 7. The LED lamp of claim 6, wherein the LED lamp isdesigned so as to satisfy 0.02 mm≦h≦0.1 mm and 0.15 mm≦x≦0.5 mm, where his the distance between the upper surface of the resin portion includingthe phosphor and that of the LED chip and x is the distance between theside surface of the resin portion including the phosphor and those ofthe LED chip.
 8. The LED lamp of claim 6, wherein the phosphor is anon-YAG-based substance, and wherein if h exceeds 0.1 mm, then the LEDlamp satisfies 0.47≦h/x≦1.82, where h is the distance between the uppersurface of the resin portion including the phosphor and that of the LEDchip and x is the distance between the side surface of the resin portionincluding the phosphor and those of the LED chip.
 9. The LED lamp ofclaim 6, wherein the resin portion including the phosphor is made of asilicone resin, and wherein the phosphor has a mean particle size of 3μm to 15 μm and has a greater specific gravity than the silicone resin,and wherein the LED lamp satisfies 0.2≦h/x≦0.5, where h is the distancebetween the upper surface of the resin portion including the phosphorand that of the LED chip and x is the distance between the side surfaceof the resin portion including the phosphor and those of the LED chip.10. The LED lamp of claim 9, wherein the resin portion including thephosphor includes particles of a thixo agent, of which the mean particlesize is less than 1 μm.
 11. The LED lamp of one of claims 1 to 10,wherein not only the LED chip but also at least one more LED chip arebonded to the substrate, and wherein each of the LED chips is coveredwith the resin portion separately.
 12. The LED lamp of claim 11, furthercomprising a reflective member with reflective surfaces that are slopedso as to reflect the outgoing light of the resin portions of the LEDchips away from the substrate, and wherein the reflective surfaces aresloped so as to surround the respective LED chips.
 13. The LED lamp ofclaim 12, wherein the reflective member is a plate having multipleopenings, each of which surrounds an associated one of the LED chips,and is provided on the substrate, and wherein the reflective member isat most twenty times as thick as the resin portion.
 14. The LED lamp ofclaim 13, wherein the reflective member has a thickness of at most 5 mm.15. The LED lamp of one of claims 1 to 10, wherein not only the LED chipbut also at least one more LED chip are bonded to the substrate, andwherein all of the LED chips are covered with the single resin portion.16. The LED lamp of one of claims 1 to 10, further comprising areflective member with a reflective surface that is sloped so as toreflect the outgoing light of the resin portion away from the substrate.17. The LED lamp of claim 16, wherein the reflective member is a plateprovided on the substrate, and wherein the reflective surface is definedby the inner wall of an opening of the plate so as to surround the sidesurface of the resin portion including the phosphor.
 18. The LED lamp ofone of claims 1 to 10, further comprising a second resin portion thatcovers the resin portion(s).
 19. The LED lamp of claim 16, furthercomprising a second resin portion that fills a gap between the sidesurface of the resin portion including the phosphor and the reflectivemember.
 20. The LED lamp of claim 18 or 19, wherein the second resinportion functions as a lens.
 21. The LED lamp of claim 1, wherein thecenter axis of the resin portion including the phosphor substantiallycorresponds with that of the LED chip.
 22. A method for fabricating anLED lamp, the method comprising the steps of (a) preparing a substrateon which at least one LED chip has been flip-chip bonded, and (b)providing a resin portion on the substrate, the resin portion coveringthe LED chip and including a phosphor that transforms the emission ofthe LED chip into light having a longer wavelength than the emission,wherein the step (b) includes the step of molding a resin material suchthat the resin portion has an exposed side surface.
 23. The method ofclaim 22, wherein the step (a) includes the step of preparing asubstrate on which multiple LED chips have been flip-chip bonded, andwherein the step (b) includes the step of covering each of the LED chipswith the resin portion separately.
 24. The method of claim 23, whereinthe step (b) includes the step of forming the resin portion in acylindrical shape.
 25. The method of claim 23 or 24, further comprisingthe step (c) of arranging a reflective member, having a reflectivesurface for reflecting the outgoing light of the resin portion, on thesubstrate after the step (b) has been performed.
 26. The method of claim25, wherein the step (a) includes the step of preparing a substrate onwhich multiple LED chips have been flip-chip bonded, and wherein thestep (c) includes the step of arranging a reflective member, having aplurality of reflective surfaces surrounding the LED chips, on thesubstrate.
 27. The method of claim 26, further comprising the step (d)of stacking a second resin portion on the resin portion including thephosphor after the step (c) has been performed.
 28. The method of claim27, wherein the step (d) includes the step of forming the second resinportion in a lens shape.